For the purpose of the invention, parts are components which are to be connected to one another and then completely detached from one another again. They include, for example, doors and door frames, couplings of hoses, ropes, rods, etc., equipment or the like to be fastened to walls, or wall panels, coverings, etc.
Similar apparatuses have been disclosed in a very wide range of variants, for example, as a truck or hood closure, or as connecting elements for two components provided with flush orifices, as described in, for example, German Offenlegungsschrift 3511070. In all these known systems, one-hand operation is possible only during closing of the apparatus, but at least a second sequence of movements is required for detaching, such as pulling on an opening lever in the case of the vehicle, or pressing a peg or the like (cf. the German Offenlegungsschrift).
It is true that there are also known apparatuses or furniture fittings which are equipped with a toggle lever mechanism and thus permit the opening and closing of doors merely by the application of pressure. These apparatuses, however, are relatively complicated to produce and have a large number of components.
Moreover, overextending the toggle lever results in some cases in a loud snapping noise which may be found unpleasant, for example, in the bedroom area.
Snap-closures having a spring-loaded locking element are also known, for example, ball catches which, although simple to operate in both directions, scarcely offer any more resistance in the opening direction than in the closing direction. The features of the relevant apparatus in the prior art are described most clearly in U.S. Pat. No. 3,039,802. Two spring lips formed as a single piece with a receiver project from the receiver at an angle to one another and lock the displacement part. During the unlocking process they are spread apart by the unlocking part, so that withdrawal of the displacement part and hence unlocking are possible. The spring lips are bent at their connection points to the base part. Thus, bending takes place at this point and, with frequent use, this may lead to weakening of the material and consequently even to fracture. In the locked stage--when the locking pins are subjected to tension--these connection points are likewise subjected to a load.
Finally, the free ends of the spring lips shear both against the displacement part and against the unlocking sleeve, with the result that material wear and undesirable abrasion may occur.
The force of the lock is difficult to adjust, since strengthening of the material simultaneously results in greater spring force and makes locking and unlocking more difficult. Further problems may arise from the leaf spring construction which opposes the locking pin. In order to possess sufficient springiness, these leaf springs must in fact be relatively long and therefore bulky. The total space requirement for the known apparatus is thus considerable, so that it is scarcely suitable for use in, for example, furniture construction. Furthermore, the leaf springs fastened on one side exert a lateral pressure on the locking pin, which may lead to jamming. Conversely, in the case of leaf springs for both sides, a locking pin inserted slightly obliquely can result in lateral tilting of the leaf springs through twisting, which then prevents them from acting in the desired manner and may lead to undesirable locking between the leaf springs and the displacement part. Locking of this type may only be capable of being undone by destruction of the entire closure. Because of their connection to the base part, it is furthermore impossible to replace or adjust the known leaf springs alone. All these disadvantages have obviously meant that the apparatus according to the US Patent has not become established in practice.